When an array of photodetectors is used to capture intensity values of an image formed by an image-sensing optical system, the final image provided to the user is generally constructed by directly assigning the intensity values that were captured to the pixels of an image matrix which reproduces the photodetector array. All the photodetectors therefore have a one-to-one correspondence to pixels in the image matrix, and intensity values captured by two adjacent photodetectors are assigned to two pixels which are also adjacent in the matrix of the final image.
Other image capture modes also exist, and the intensity values that are captured are assigned to the pixels of the final image matrix in a manner adapted to each capture mode. In particular, when a scene is captured in push-broom mode, the final image is reconstructed by assigning, to the pixels of different segments of the final image matrix, intensity values which were captured at different times as the scene is scanned by the image capture system. Such a push-broom capture mode is used in a scanner or photocopier, for example. It is also known to use push-broom mode to photograph portions of the Earth's surface from a satellite. In this case, a portion of the Earth's surface is scanned as the pointing direction of the image-sensing optical system advances.
However, in such a push-broom capture mode, adjacent pixels of the final image reproduce unit regions of the photographed scene which are separated by the dimension of a photodetector, divided by the enlargement of the image-sensing optical system for the image capture conditions used. For the Earth imaging application, this distance separating two unit regions of the Earth's surface reproduced in neighboring pixels in the final image matrix is called ground sampling distance (GSD) or ground resolution.
Another characteristic of imaging methods is the modulation transfer function, commonly referred to as MTF. It is equal to the quotient of the contrast of a periodic modulation in the final image divided by the actual contrast of this modulation in the photographed scene. The value of the modulation transfer function decreases when the spatial frequency of the modulation increases. The value of the modulation transfer function is limited by several effects, including effects of the image-sensing optical system and of the photodetectors used. In particular, increasing the diameter of the entrance pupil of the image-sensing optical system increases the modulation transfer function. Conversely, non-zero individual dimensions of photodetectors and a possible crosstalk occurring between neighboring photodetectors contributes to reducing the modulation transfer function. Obtaining a modulation transfer function which has high values is desired, particularly for earth imaging applications.